Autoclaves and cryoautoclaves already exist in which an experimental volume is defined capable of being subjected to temperatures as high as 500.degree. K. and to pressures as high as 3000 bars. However, these devices cannot be used for studying transient phenomena, since they are completely closed and microscope observation is impossible, so that observations are reduced merely to the ambient pressure and temperature conditions under which the sample for investigation is recovered. The German patent application published under the number 2 022 810 may be mentioned as an example.
A stage assembly has been proposed for observing transient phenomena, but for which temperature is the only physical parameter. This stage assembly comprises an oven having a copper tube suitable for passing liquid nitrogen wound thereabout , together with an optical condenser located in a ring. In addition to the above-mentioned limitation, this stage assembly operates solely at atmospheric pressure, so that its thermal insulation is inadequate at high temperatures. Nevertheless, this stage assembly is advantageous because of the accuracy of its measurements, since it uses ceramic-covered platinum probes for measuring temperature. A stage assembly of this type is shown in U.S. Pat. No. 3 969 013.
The stage assembly of the present invention seeks to cover wide ranges of variation in the physical parameters, in particular, it seeks to cover temperatures in the range 77.degree. K. to 800.degree. K. and pressures in the range 1 bar to 3000 bars.
Considerable difficulties appear when investigating the possibility of varying these two parameters over such wide ranges, because of the very small size of the experimental volume.
Thus, prior stage assemblies have been adapted, above all, to cope with large ranges of temperature variation only.
U.S. Pat. No. 3 472 726 describes a stage assembly through which light may be passed, and including an open disposed in an enclosure having an opening to the outside, said opening is necessary for air cooling, and the air is mixed by means of a fan.
British Pat. No. 1 375 193 describes another type of specimen stage which does not allow light to pass therethrough and which includes means for rapidly setting up desired temperature values. It mentions as a subsidiary point that the gaseous atmosphere in the experimental volume may be modified, but for the sole purpose of varying the type of gas for temperature measurements. This has nothing to do with considering pressure as one of the physical parameters which may be varied over a very wide range, and in addition, the structure of its rotating cover is quite unsuitable for large pressure variations.
Finally, existing devices do not allow obervations to be made under a microscope with the parameter conditions associated with the above-mentioned wide ranges. Nevertheless, such observations would be very useful in many disciplines, for example solid state physics, geology, biology, organic and inorganic chemistry, thermodynamics, crystallography, mineralology, etc. . .
The main object of the invention is to provide a stage assembly which is sufficiently isolated from the optical equipment to enable phenomena to be observed over temperature and pressure ranges which may be as great as those mentioned above, without requiring fundamental alterations to the structure of the optical equipment.
Another object of the invention is to make it possible to use such a stage assembly with a conventional microscope, even though presently available sizes make it impossible to use a conventional microscope at maximum magnification.
Another object of the invention is to make it possible to operate in vacuo, thereby providing improved isolation during an experiment, and consequently providing greater stability in the ranges for thermodynamic study.